using System;

​

​

public abstract class SimpleCalculator

{

    public abstract double Calculate(double a1, double b2);

}

​

public class Addition : SimpleCalculator

{

    public override double Calculate(double a1, double b2)

    {

        return a1 + b2;

    }

}

​

public class Subtraction : SimpleCalculator

{

    public override double Calculate(double a1, double b2)

    {

        return a1 - b2;

    }

}

​

public class Multiplication : SimpleCalculator

{

    public override double Calculate(double a1, double b2)

    {

        return a1 * b2;

    }

}

​

public class Division : SimpleCalculator

{

    public override double Calculate(double a1, double b2)

    {

        return a1 / b2;

    }

}

​

​

​

​

public class Calculator

{

    private SimpleCalculator operation;

​

    public Calculator(SimpleCalculator operation)

    {

        this.operation = operation;

    }

​

    public double PerformCalculation(double a1, double b2)

    {

        return operation.Calculate(a1, b2);

    }

}

​

public class Program

{

    public static void Main()

    {

        // ...

​

        bool continueCalculating = true;

​

        while (continueCalculating)

​

        {

        First:

            Console.WriteLine("-----------------");

            Console.WriteLine("Basic Calculator");

            Console.WriteLine("-----------------");

​

            Console.Write("\nEnter the first number: ");

            double number1 = Convert.ToDouble(Console.ReadLine());

​

            Console.Write("Enter the second number: ");

            double number2 = Convert.ToDouble(Console.ReadLine());

​

        success:

            Console.WriteLine("\nSelect operation:");

            Console.WriteLine("[1] Addition");

            Console.WriteLine("[2] Subtraction");

            Console.WriteLine("[3] Multiplication");

            Console.WriteLine("[4] Division");

            Console.Write("Enter your choice of operation ([1] or [2] or [3] or [4]): ");

            int choice = Convert.ToInt32(Console.ReadLine());

​

            SimpleCalculator operation;

            switch (choice)

            {

                case 1:

                    operation = new Addition();

                    break;

                case 2:

                    operation = new Subtraction();

                    break;

                case 3:

                    operation = new Multiplication();

                    break;

                case 4:

                    operation = new Division();

                    break;

                default:

                    Console.WriteLine("Sorry, Invalid Selection. Only range of 1...4 are expected");

                    Console.WriteLine("Please try again.");

                    goto success;

            }

​

            Calculator calculator = new Calculator(operation);

            double result = calculator.PerformCalculation(number1, number2);

            Console.WriteLine();

            Console.WriteLine("Result: " + result);

​

            Console.Write("\nDo you want to try another operation? (Y/N): ");

            string input = Console.ReadLine();

            if (input.Equals("N", StringComparison.OrdinalIgnoreCase))

            {

                Console.Write("\nTHANK YOU");

                return;

            }

        }

    }

}

​